Mixing pump



Jan. 8, 1952 Filed Sept. '14, 1949 M.B.SENNET MIXING PUMP 4 Sheets-Sheetl FT F l HVVENTOR. MORGAN 5.. SENNET j ATTDRN Y5 M. B. SENNET MIXINGPUMP Jan. 8, 19 52 4 Sheets-Sheet 2 Filed Sept. 14, 1949 FIG. 2.

INVENTOR. MORGAN B. SEN/VET ATIORNE s Jan. 8, 1952 M. B. SENNET 1 MIXINGPUMP Filed Sept. 14, 1949 4 Sheets-Sheet 5 I INVENTOR. 'F/G. 5. MORGANB. SEA/N57 AT TORNEYS.

Jan. 8, 1952 I SENNET M 2,581,451

MIXING PUMP Filed Sept. l4. 1949 4 Sheets-"Sheet 4 INVENTOR. F/ 6. ZMORGAN B. SEI VNET ATTORNEYS.

Patented Jan. 8, 1952 UNITED STATES PATENT OFFICE MIXING PUMP Morgan B.Sennet, Trenton, N. J., assignor to i I De Laval Steam Turbine Company,Trenton, I N. J., a corporation of New Jersey Application September 14,1949, Serial No. 115,671

13 Claims. 1

This invention relates to a mixing pump particularly designed for theeffective mixing or kneading of materials of a fluent or viscous type,the pump being of a multiple screw type.

The effective mixing of paints or other suspensions of solid, semisolid,or liquid materials in liquids to provide homogeneous products isgenerally a rather diflicult and time consuming operation for whichordinary Stirring or other agitation in batches will frequently notsuflice to give the desired products. In accordance with thepresentinvention the mixture of constitucnts'is subjected to flowthrough tortuous paths provided between cooperating rotating screwsinvolving kneading action which is extremely effective in producinghomogeneity.

In the patent to Montelius 1,698,802, dated January 15, 1929, there isdisclosed a type of screw pump which is positive in its displacementcharacteristics. Positive screw pumps of this type have gone intowidespread use and are capable of operating at quite high speeds. A pumpof this positive displacement type if fed with a solid-liquid mixture orwith a mixture of liquids which are not mutually soluble in the proportions used will promote mixing to some extent due to therelative motionsof the screw surfaces and housing surfaces with respect to the materialtrapped in the travelling chambers of the pump. However, since theportions of the material are carried through .the pump effectively intheform of individual slugs of substantially fixed shape from thestandpoint of their boundaries the mixing is not particularly effectiveand, in fact, much of the efliciency of these pumps is due to thefashion in which the liquid is advanced with a minimum rather than amaximum of turbulence imparted thereto.

In the 'Montelius patent referred to above there are discussed therequirements on the relationships between the numbers of threads onintermeshing screws required for the attainment of positivedisplacement. A violation of these requirements will result in aninherent nonpositive characteristic of a screw pump provided withintermeshing screws even though the thread'shapes are generated inaccordance with the principles of the patent, and irrespective of theetiectiveaxial length of the pump which may be defined as the lengthwhich involves interis attempting to effect pumping action.

meshing of screws within intersecting bores in I l 2 accordance withdeparture from the principles established for positive screw pumps andsuch a non-positive pump is used for the pumping of a mixture with theobject of providing homogeneity, more effective mixing is produced thanwould be produced by a positive screw pump of comparable length providedthe pumping takes place against a substantial head. In contrast with apositive screw pump the pumping action of such a non-positive screw pumpis dynamic in character, i. e., the material is progressed through thepump by virtue of a propelling action of the screws since no closedchambers are formed and if the pump is stopped the material will fiowfrom the high pressure end of the pump through the low pressure end.Slippage of the material is accordingly an inherent characteristic ofsuch a non-positive pump: i. e., the ad-' vance of the material pumpedis always less than what might be considered the theoreticaldisplacement of the pump involving no retrograde movement of thematerial relative to the screw threads. The fact that such slippageoccurs accounts for the increase in eiiectiveness of mixing, inasmuch asthe material, as it is progressed through the pump, has a greater amountof relative slippage with respect to the screws than would be the casein a comparable positive pump of the same effective screwlength.

In accordance with the present invention the mixing effect is verygreatly increased by combining a positive pump with a non-positive screwpump in such fashion as to drive the material undergoing admixture in adirection contrary to the direction in which the non-positive pump Thepositive pump which is used may be of any type to eiTect reverse flowthrough the non-positive screw pump but, as will hereafter appear, theinvention lends itself to embodiment in a simple and highly effectivemixer involving the combination of a positive pump and a non-positivepump both of screw type which may be in the same housing and may havecommon shafting to reduce to a minimum the problem of providingsimplicity of drive, provision of proper bearings, small size, etc.

, The invention, however, is not confined to a non-positive screw pumpopposing a positive one. Similar effective results may be secured byopposition of a pair of non-positive pumps one of which has a moreeffective pumping action than the other so as to force the mixture inretrograde direction through the latter. As will appear hereaftervarious such combinations of pumps may be provided.

The broad object of the invention in providing an effective mixingdevice has been indicated above. The attainment of this object as wellas the attainment of various other objects particularly relatingtodetails of construction and operation will become apparentfrom thefollowing description read in conjunction with the accompanyingdrawings, in which:

Figure 1 is an axial section through a mixer illustrating one preferredembodiment of the principles of the invention;-

Figure 2 is a transverse section takenuon': the plane indicated at 2-2in Figure 1;

Figure 3 is a transverse section taken on the plane indicated at 33 inFigure 1;

Figures 4, 5, 6 and 7 are diagrams which clarify the nature of the flowpaths of the types herein involved; and V Figure. 8 is asection similarto Figure 2 but showing anentrance sand/or exit arrangement for thenon-positive mixing pump to promote mixing action.

Referring first to Figures 1, 2 and 3, the mixing pump comprises a casin2 havingan inlet opening 4 and an outlet opening 6. The former maycommunicatewith a'source of roughly admixed material which is to betransformed into a homo-, geneous mixture, while the latter may communicate with a receiver- If more than onepass of themixture through the;apparatus is required to -secure the necessaryhomogeneity the receiverand-.source'may bemerged intoone receptacle through which the pump willproduce recirculation to proces a batch of material. As will be evident,various circuits external to the pump may beprovided such as are commonin connection with other mixers and these circuits form no specialpartof the present invention, vwhichis concerned primarily with what occursto the mater-ialfrom the entrance 4 and the exit 6. Liners 8 and 10contained within the casing 2 provide housings fora positive multiplescrew pumpindicatedgenerally at I 2 .and a non-positive multiple screwillustrated generally at [4. A shaft I6 has mounted thereon, or, asshown, cut thereon, a power screw [8 for thepositive pump and 'a powerscrew fora non positive pump. As specifically indicated inthe drawingseach of these screws contain two threads with the threads of therespectivescrews of opposite hands. Meshing with the power screws areso-called idler screws formed oncommonspindles or shafts indicated at 22and 24. Theidler screws meshing with the screw 3 of. the positive pumpare indicated at 26 and 28. The idler screws meshing with the powerscrew 20 of the non-positive pump and formed on shafts 22 and 24: areindicated atv 3fl and 32. In addition to the idler screws 30 and 32there mesh with thescrew 2!! of 'thenonpositive pump another pair ofidler screws 34 and -36. As will be evident, to provide meshing theidler screws 30, 32-, 34-and 36 are of a hand opposite that of the idlerscrews2B and '28.

'Inthe-arrangement illustrated all of the idler screws are of two-threadtype and except for their hand all of these idler screws are preferablyidentical. Both the power screws *and idler screws aredesigned inaccordance with 'the'principles set forth insaid Montelius patent sothat, when assembly is provided, as indicated in Figure 3 in the case ofthe positive. pump I2, a conventional region provided by a spacercylinder 40., the interior 42 of which provides a conduit for thepassage of material from the positive pump to the non-positive pump.Bearings of suitable type are provided at 46 and 4B for mounting andtaking the end thrusts of the various screws. The

screws have additional mounting in the bores in their housings ,8 andH), the former having two side bores for. thereception of the positivepump idler screws and the latter having four side boresforithenon-positive pump idler screws. The clearances of the screws withtheir mounting bores are quite small, being exaggerated .in Figureszand3..

As will be evident from consideration of the figures, a rotation. of theshaft. [6 in'the directionv of the-arrow will causethe positive pump tooperate to drive the pumped material from the right toward the left. Thenon-positive pump I4, on" theother hand,,is so operated as to tend to.drive the material from the left toward the right;

' However, being non-positive this lastpump must yield tothe action ofthe positive pump so that despite theeffort which it exertsthe materialwill flowv therethrough from the righttoward the.

pump is provided suchas is commonly used for high speed positivepumping. Desirably the left. From the standpoint of pressures producedit, will be evident that this operation will giverlse to a very highpressurein the space .42...v The overall pressure of the pump from.inlet toroutlet will depend upon the head which is pumped against andwhich, in most uses of the pump; would be relatively low. The-shaft 6and the idlers carried. by the shafts .22 and 24 will have a net. thrusttoward the right but this is generally relatively low and simple thrustbearing arrangements will suffice to. take care of thisthrus-t. On theother hand, the thrusts on thescrews 3.4.:and 36 will be towardthe leftand quite, large softhat as. indicatedthe bearing arrangementat 46 mustbe of a typesufiicient to. resist this left hand thrust of these screws.

As will beeVident, the non-positive pump will produce an intenseturbulence and shearing. mix! ing action, on thematerial passingtherethrough since an extreme relative motion of the material with.respect tothe screws is. provided dueto-the fact that thescrews areoperating to oppose the flow of material forced by the positive-pump.The mixing action is. greatlyincreased, further? more, by the tortuous.path of the material throughthe non-positive pump To explain this, and.in. particular, the relative characteristicslof differentkinds ofnon-positive pumps-reference may bemade to Figures 4, 5, 6 and '7'which-respectivelyindicate the characteristics of:opera,- tion of apositive pump having two idlers, a non;- positive :pump having threeidlers, a rnon-posi tive pump'zhaving. four idlers,1and a non-positivepump. :h-avingtfive. idlers, in each. case there being apower screwhaving two threads and idlers each having two threads. v i

The various diagrams of Figures 4, 5; Sand 7 may-berbest understood byconsidering thatthey represent, from a purely diagrammaticstand point,sections of slightly more than a complete circuit about the power screwin e'achca'se. These diagrams may be best 'understoodby considering thediagram of Figure 6 with reference to Figure 2, the diagram being adevelopment of a section taken on an axial surface just inside theperipheries of the screws along a path. from an about the outer portionof idler 39 to :02, thence to 3:3 about the power screw 20, thence aboutidler 34 to 11:4 and similarly about the power screw and the otheridlers to axial lines as, rs, m1 and x8, and finally back to an. Thesegmental sections of the power screw are then indicated at P, while thesegmental sections of the idler screws are indicated at the Is providedwith subscripts corresponding to the various idlers provided. Figures 4,5 and '7 are sections taken in similar fashion. V

Continuing thereference to Figure 6, the form of pump having fouridlers, assume'rotation of the power screw in the direction of the arrowat the top of Figure 6. Under this assumption the inletto the pump willbe at the bottom of the figure and the outlet will be at the top of thelengths of the screws this path will be continuously open and willprovide a tortuous leakage path from the outlet end of the set of screwsto theirinlet end. Furthermore, since the leakage path is duplicatedthere are, in effect, two parallel leakage paths preventing the pumpfrom operating in a positive fashion. These paths, however,-are sotortuous, as may be recognized particularly by reference to Figure 2,that the pump has a very effective dynamic action and, if of properlength, is capable of producing a quite substantial head.

Consideration may-now be given to the question of proper length of thescrews. By length is meant the effective length through which thescrews-are in mesh and arealso properly surrounded by the housing toform a closed path.

By considering the contacts between the screws it will be found that,first assuming a symmetrical arrangement of the idlers about the powerscrew, 9. complete circuit of the power screw by the liquid to follow aleakage path will be required if the effective length of the pump, asabove deffined, is given by the following equation:

in which, assuming a single power screw,

-' M is the minimum effective length of mesh and enclosure of the screwsto insure that liquid passing from outlet to inlet must make at least acomplete circuit of the power screw;

P is the pitch, equal to the lead of each screw divided by the number ofits threads;

N is the number of idlers; V

m is the number of threads on each idler;

. up is the number of threads on the power screw; and, l' Wis the axialwidth of the top of the power screw.

If the minimum effective length is less than this, it will'happen thatin some positions of the screws a path may be found from'outlet to inletwhich will make less than a complete circuit of the powerscrew. Thispossibility is undesirable giving not only an absence of fulleffectiveness of the screw arrangement in terms of producing maximumhead for a given speed of operation, but will also give rise topulsations by virtue of the less effective pumping action whenever thescrews attain a configuration which gives the shorter path justmentioned.

As an application of the foregoing formula, the following tabulationindicates the: values of M for pumps having a single power screwcarrying two threads and two, three, four and five idlers, respectively,each carrying two threads:

The assumption of a minimum effective pump length for a symmetricalarray of idler screws applies, however, to an asymmetrical array, sinceit will be found that, if an asymmetrical array is used, the minimumlength would have to be greater than that given by the above formula toavoid a leakage path in certain positions of the screws which wouldprovide less than a complete circuit of the power screw. Actually,symmetrical arrays are most desirable to avoid the existence ofunbalanced lateral thrusts on the screws.

Attention may now be given to Figures 4, 5 and 7 which indicate thenature of the paths or chambers existing when two, three and fiveidlers, respectively, are used.

Figure 4 is provided only for completeness of the systematic disclosure.It represents a positive pump comprising a power screw of two threadsmeshing with two idlers of two threads each, this being the positivepump illustrated in Figure 1. If the path CD is noted, it will be seenthat it starts andends in the same groove position. Accordingly, it doesnot extend axially and this path represents a closed chamber making thepump positive. The expression given for M, however, still applies and inthis case has a significance that the effective length of the pumpshould be as indicated in the foregoing tabulation to-insure thatthepump will actually be positive.

Referring to Figure 5, which shows a three idler arrangement it will benoted that the path EF, corresponding generally to the path AB of Figure6, completes a circuit of the power screw in the next lower groove belowthe startin groove E. Since the value of M for this pump is less thanfor the four-idler pump, and only a single pathis provided, it will beevident that for given screw dimension and for given speed of operationa greater head may be produced with the threeidler arrangement than withthe four-idler arrangement with, however, a reduction in capacity.

The five-idler arrangement is illustrated in Figure '7, the free leakagepath being indicated at GI-I. It will be noted that this path makes acircuit of the power screw dropping to the third groove below itsbeginnin at the end of this circuit. This means that there will be threeparallel paths running through the screws, the additional two paths, forexample, passing through G and G". As pointed out in Montelius Patent1,698,802 a positive pump is provided by a power screw having one threadmeshing with a single idler screw having two threads. From thisconstruction a non-positive pump may be derived merely by adding anotheridler of the two thread type; Numerous other non-positive pumps may be.derived by departure from the conditions given in said Montel-ius Patent1,698,802. for positive screw pumps.

It may be noted that the. formula given above for M applies to such.pumps in general provided with a single power. screw, and from thisthere maybe determined the minimum-effective pump length forgbestutilization of..any such screw arrangement.

It will also be evident that non-positivescrew pumps may be derived'frompositive screw pumps merely be decreasing'the circumferential extents ofthe threads of the power or idler screws so as to afford clearanceswhich will prevent complete closures of pockets which would normallyexist in positive pumps, though this modification is not recommendedsince it permits play between the screws and weardue to impact unlesstiming gears are added.

In all the cases referred to above effective mixing can be attained bycausing flows to take place in directions opposite the flows through anonposi't'ive pump.

It will also be evident that imposing reverse flow through anon-positive pump maybe secured by causing two non-positive screw pumpsto buck each other if one is of a typeiproducing a dynamic propellingcharacteristic in-iexcessof that of the other. As an. example, a 3-idlerpump of the type diagrammed in Figure 5 may be arranged tov oppose theflow through a i l-idler pump of the type illustrated in.Figure 6; Inthis, case for the same or comparable lengthsof the pump 3 the 3-idlerpump will overcome the 4-idler pump so as to. enforce a reverse flowthroughthe latter. At the same time a considerable degree-of admixingaction will occur in the 3-idler pump due to slippage therein. Thearrangement may also be reversed so that a i-idler pump overcomes a3-idler pump by making the screws ,of the former sufficiently long.

Furthermore, two similar. non-positive pumps of the same type, from thestandpoint of num- .bers of screws and threads, maybe arrangedto oppose.each other if they are of diiferent lengths so'that the longer of themwillproduce a head greater than the shorter.

Similar results may also be secured by the opposition of screw pumps ofthe same or different types having different pitches" of'their threadsso that one of them may overcome the action of the other. As will beevident, avery great variety of screw pumps may be combined toattalnmixing actions in accordance with the principles of the invention.While the opposition of a pair; of screw pumps is particularly desirablein carrying-out the in vention, it may be noted that it" is'thereverseflow through a non-positive pumpwhlchis-particularly responsible foreifective mixing;- the pump which produces the reverse flowithrofugh'the mixing pump has primarily only thefunction of producing that flowand, consequentlylmaybe replaced by other positive pumps. or by suchnonrpositive pumps as may-be capable of. producing the reverse flow asdescribed. When-,1 as usual,

viscous materialsare being mixedit may bend-ted that the non-positivescrew. pumps which. have been described actually, are capable of.producing very substantial heads and,; consequently,; the pump whichenforces reversefiowmust; becapable, of producing, even .greaterheads.Another screw pump. isv particularly.applicable for this purpose and,furthermore: the use of aspair of screw pumps; results. .in thepractical: advantage entrance to the. screws of the non-positive pump,

and. .exit therefrom takes place axially, i.e.,;.the ends of .athescrews are completelyopentoaenq trance =and-exit chambers. An augmentedmixing.

action may. be produced in; accordance-.withtthe arrangementillustratedin Figure 8 which applies to: bothzthe entrance and .ex-itends-of thescrews. In this modification, the ends of thescrewssmay be .confined andentrance of the mixture tosthe screws andexitafrom the screws may beprovided through. radially extending openings Elsi-n, the ends:otthe-houslng 50 for the screws IDA- 3 113 32"., 34" and536" whichcorrespond to the similarly numbered screws inFigures .1 and 2. vIt willbe evidentthat the screw threads will cut across suchopeningszandqaccordingly effect a chopping actionz onthe entering orleavingmixtura. If the pump is operating at high speed, this choppingaction is, particularly efiective to produce a breaking up of anyagglomerates 01 solid material or concentration of liquid droplets,which may existdn the .mixture. The screws should ..desirablybe :of.such lengths exceeding the.mini mum. effective lengths discussed aboveso.-- that theopenings v52 at the entrance and exit-are spacedby morethan this effective. length;

What I claim.- and desire. to protect by Letters Patent is:

1.2111119. mixing device, in combination; anon; positivemultiple screwpumpincluding a power serew=andatleast zone idler screw,., a secondmultiple. screw pump including a power screw andat. leastone. idlerscrew, said power screws being ooaxiallyemounted and. rotating togetherand said idler screws being coaxially-mounted androtating together, saidpumps having a-common housing. and said second pump being consstructedand arranged to force afl-uent mixture through the firstmentioned pump in a. direction opposing-the-pumping action of the-firstmene irioned pump. 7

2.1 In amixing device, .in combination, a anonpositive multiple screwpump including a power screw and at least one, idler screw, asecond-positivermultiple screw pump; including a power-screw andatleastone: idler; screw,,said power screws being coaxially mounted and.rotating together and said idler screws being coaxially mounted androtating together.,-.said pumps havinga'common housing, and said secondpump-being constructed and arranged ,to forcea fluent mixture throughthe first mentioned pump-in a direction opposing the pumping'action oi.the firstgmentioned pump;

3. Ina mixing--device,1 in combination, anion-'- positiv e multiplescrew pump including a power screw having two threads and at leastthree, idler screws, each having two threads, asecond multiple screwpump-including apowerscrew having two threads. and at leasttwoidlerscrews; each having two threads, said power screws belng scosaxially. mounted and rotating, togethenzand each of said idler screws ofthe second mentioned pump being coaxial. with',.and rotatingrwith, acorresponding idler :screvr of the first, mentioned pump, said secondpump being constructedand arranged to force a fluentmixture.throught..-the

-.firs,t mentionedpump in a direction -opposi-ng 4. In a mixing device,in combination, a nonpositive multiple screw pump including a powerscrew having two threads and at least three idler screws, each havingtwo threads, a second positive multiple screw pump including a powerscrew having two threads and two idler screws,

each having two threads, said power screws being coaxially mounted androtating together, and each of said idler screws of the second mentionedpump being coaxial with, and rotating with, a corresponding idler screwof the first mentioned pump, said second pump being constructed andarranged to force a fluent mixture through the first mentioned pump in adirection opposing the pumping action of the first mentioned pump.

5. In a mixing device, in combination, a nonpositive multiple screw pumpincluding a power screw having two threads and four idler screws, eachhaving two threads, a second multiple screw pump including a power screwhaving two threads and at least two idler screws, each having twothreads, said power screws being coaxially mounted and rotatingtogether, and each of said idler screws of the second mentioned pumpbeing coaxial with, and rotating with, a corresponding idler screw ofthe first mentioned pump, said second pump being constructed andarranged to force a fluent mixture through the first mentioned pump in adirection opposing the pumping action of the first mentioned pump.

6. In a mixing device, in combination, a nonpositive multiple screw pumpincluding a power screw having two threads and four idler screws, eachhaving two threads, a second positive multiple screw pump including apower screw having two threads and two idler screws, each having twothreads, said power screws being coaxially mounted and rotatingtogether, and each of said idler screws of the second mentioned pumpbeing coaxial with, and rotating with, a corresponding idler screw ofthe first mentioned pump, said second pump being constructed andarranged to force a fluent mixture through the first mentioned pump in adirection opposing the pumping action of the first mentioned pump.

7. In a mixing device, in combination, a nonpositive multiple screw pumpincluding a power screw having two threads and four idler screws, eachhaving two threads, a second positive multiple screw pump including apower screw having two threads and two idler screws, each having twothreads, said power screws being coaxially mounted and rotatingtogether, and each of said idler screws of the second mentioned pumpbeing coaxial with, and rotating with, a corresponding idler screw ofthe first mentioned pump, said two power screws being of opposite hands,said second pump being constructed and arranged to force a fluentmixture through the first mentioned pump in a direction opposing thepumping action of the first mentioned pump.

8. In a mixing device, in combination, a nonpositive multiple screw pumpincluding a power screw and at least one idler screw, means for drivingsaid pump, and a second pump for forcing a fluent mixture through thefirst mentioned pump in a direction opposing the pumping action of thefirst mentioned pump.

9. In a mixing device, in combination, a non positive multiple screwpump including a power screw and at least one idler screw, means fordriving said pump, and a second positive pump for forcing a fluentmixture through the first mentioned pump in a direction opposing thepumping action of the first mentioned pump.

10. In a mixing device, in combination, a nonpositive multiple screwpump including a power screw and at least one idler screw, means fordriving said pump, and a second positive multiple screw pump including apower screw and at least one idler screw for forcing a fluent mixturethrough the first mentioned pump in a direction opposing the pumpingaction of the first mentioned pump.

11. In a mixing device, in combination, a nonpositive multiple screwpump including a power screw and at least one idler screw, a secondmultiple screw pump including a power screw and at least one idlerscrew, said pumps having a common housing and a common drive shaft, andsaid second pump being constructed and arranged to force a fluentmixture through the first mentioned pump in a direction opposing thepumping action of the first mentioned pump.

12. In a mixing device, in combination, a nonpositive multiple screwpump including a power screw and at least one idler screw, a secondpositive multiple screw pump including a power screw and at least oneidler screw, said pumps having a common housing and a common driveshaft, and said second pump being constructed and arranged to force afluent mixture through the first mentioned pump in a direction opposingthe pumping action of the first mentioned pump.

13. In a mixing device, in combination, a non positive multiple screwpump including a power screw and at least one idler screw, means fordriving said pump, and a second multiple screw pump including a powerscrew and at least one idler screw for forcing a fluent mixture throughthe first mentioned pump in a direction opposing the pumping action ofthe first mentioned pump.

MORGAN B. SENNE'I.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

